The Transmission Control Protocol/Internet Protocol (TCP/IP) suite is a basic and common communication format of the Internet, and has a two-layer structure, which is a subset of the Open Systems Interconnection (OSI) reference model. The higher layer, TCP, manages the assembling of messages (e.g., files) into packets that are transmitted over the Internet and received by a TCP layer at the message's destination, which reassembles the packets back into the original message. The lower layer, IP, handles the addressing of each such packet to ensure that the packet reaches the correct destination. Often, TCP/IP uses a client/server model of communication, in which a computing device such as a mobile station (i.e., a client) requests and is provided a service by another computing device (i.e., a server).
TCP/IP is used by many Internet applications, including the World Wide Web (WWW), e-mail, File Transfer Protocol (FTP), Secure Shell, and some streaming media applications, among many other examples. In general, then, devices such as mobile stations may be arranged to execute data applications that use TCP to connect with other devices. When used by an upper-layer application, the TCP layer maintains what is known as a TCP connection to verify that all packets in a message have been properly received and acknowledged by their intended recipient. A TCP connection typically involves three phases: a connection-establishment phase, a data-transfer phase, and a connection-release phase. To establish a connection and thereby begin the connection-establishment phase, TCP uses a three-way handshake. This handshake comprises: (1) an active open (involving the client sending what is known as a SYN to the server), (2) in response, the server replies with what is known as a SYN-ACK, and (3) the client sends an ACK (acknowledgment) back to the server. At this point, both the client and the server have received an acknowledgement of the connection. After the connection has been established, data is transferred. The connection-release phase begins after the data has been transferred.
With respect to air-interface communications (using the physical and Media Access Control (MAC) layers of the OSI reference model to exchange packets assembled by TCP and addressed by IP), mobile stations generally have two modes of operation: (1) connected mode and (2) idle (or sleep) mode. In connected mode, a mobile station wirelessly transmits and/or receives application data. Furthermore, in connected mode, even if the mobile station is not transmitting or receiving any application data, its power consumption is relatively high as a result of power being used for transmitting and/or receiving signaling messages. When a mobile station is in connected mode and no application-data packets are transmitted or received for a timeout period such as a few seconds (i.e., until expiration of what is known as and referred to herein as a mobile station's inactivity timer, which is reset each time an application-data packet is sent or received), the mobile station will transition to idle mode to conserve power. The power consumption in idle mode is much lower than it is in connected mode, as no application-data packets are sent or received, and the number and frequency of signaling messages that are sent and received is small by comparison to connected mode.